Tutorial: 4.2. for Statements

[Derangedn00b]

BPO	38058

^{Note: these values reflect the state of the issue at the time it was migrated and might not reflect the current state.}

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assignee = None
closed_at = <Date 2019-09-08.16:17:16.279>
created_at = <Date 2019-09-08.16:13:34.921>
labels = ['invalid', 'build', '3.7', 'docs']
title = 'Tutorial: 4.2. for Statements'
updated_at = <Date 2019-09-08.16:17:16.279>
user = 'https://bugs.python.org/Derangedn00b'

bugs.python.org fields:

activity = <Date 2019-09-08.16:17:16.279>
actor = 'Derangedn00b'
assignee = 'docs@python'
closed = True
closed_date = <Date 2019-09-08.16:17:16.279>
closer = 'Derangedn00b'
components = ['Documentation']
creation = <Date 2019-09-08.16:13:34.921>
creator = 'Derangedn00b'
dependencies = []
files = []
hgrepos = []
issue_num = 38058
keywords = []
message_count = 1.0
messages = ['351331']
nosy_count = 2.0
nosy_names = ['docs@python', 'Derangedn00b']
pr_nums = []
priority = 'normal'
resolution = 'not a bug'
stage = 'resolved'
status = 'closed'
superseder = None
type = 'compile error'
url = 'https://bugs.python.org/issue38058'
versions = ['Python 3.7']

[Derangedn00b]

>>> # Measure some strings:
... words = ['cat', 'window', 'defenestrate']
>>> for w in words:
...     print(w, len(w))
...
cat 3
window 6
defenestrate 12

If you need to modify the sequence you are iterating over while inside the loop (for example to duplicate selected items), it is recommended that you first make a copy. Iterating over a sequence does not implicitly make a copy. The slice notation makes this especially convenient:

>>>>>> for w in words[:]:  # Loop over a slice copy of the entire list.
...     if len(w) > 6:
...         words.insert(0, w)
...
>>> words
['defenestrate', 'cat', 'window', 'defenestrate']

words is a tuple and is immutable